The invention relates to composite nonwoven fabrics, and more particularly to extensible nonwoven composite fabrics which are capable of elongating during mechanical stretching and which have excellent surface abrasion resistance.
Composite nonwoven fabrics are used in a variety of applications such as garments, disposable medical products, diapers and personal hygiene products. New products being developed for these applications have demanding performance requirements, including comfort, conformability to the body, freedom of body movement, good softness and drape, adequate tensile strength and durability and resistance to surface abrasion, pilling or fuzzing. Accordingly, the composite nonwoven fabrics which are used in these types of products must be engineered to meet these performance requirements.
In Sabee, U.S. Pat. Nos. 4,153,664 and 4,223,063, it is disclosed that the softness and drapeability of composite nonwoven fabrics, formed for example from a meltblown or a spunbonded nonwoven fabric, can be improved by drawing or stretching the fabric. More particularly, according to Sabee, the composite nonwoven fabrics are processed by differentially drawing or stretching the web to form a quilted pattern of drawn and undrawn areas, providing a product with enhanced softness, texture and drapeability. However, while the stretching may improve some fabric physical properties, it can adversely affect other important properties, such as abrasion resistance, for example, leaving the fabric with an unsightly fuzzed surface. In addition, Sabee teaches the use of undrawn or underdrawn filaments in the use of this application. Undrawn or underdrawn filaments are typically higher in denier and therefore the fabrics tend to be stiff.
Often, the performance requirements of the product demand a composite nonwoven fabric having elasticity. In certain disposable diaper designs, for example, it is desired to impart elastic properties to the waist and/or to the leg cuff areas. One approach which has been taken to providing such elastic properties in a composite nonwoven fabric involves forming and stretching an elastic web, then bonding a gatherable web to the elastic web, and relaxing the composite. An obvious limitation of this approach is having to form the composite in the tensioned state. This requires additional equipment and control systems. Examples of this process are Mormon, U.S. Pat. No. 4,657,802, where it is disclosed that a composite nonwoven elastic is made by first stretching an elastic web, forming a fibrous nonwoven gatherable web onto the stretched elastic nonwoven, joining the two together to form a composite structure, then allowing the composite to relax. In Collier, et al., U.S. Pat No. 5,169,706, it is disclosed that a composite elastic material having a low stress relaxation is formed between an elastic sheet and a gatherable layer. In Daponte, U.S. Pat. No. 4,863,779, a composite is disclosed which involves first tensioning the elastic elastic web to elongate it, bonding at least one gatherable web to the elastic web, and relaxing the composite immediately after bonding, so that the gatherable web is gathered between the bond points.
Another approach to imparting elastic properties to a composite nonwoven fabric is with a so-called xe2x80x9czero-strainxe2x80x9d stretchable laminate. A xe2x80x9czero-strainxe2x80x9d stretchable laminate refers to a fabric in which at least two layers of material, one elastic, the other substantially inelastic, are secured to one another along their coextensive surfaces while in a substantially untensioned state. The fabric is subsequently subjected to mechanical stretching. The inelastic layer typically fractures or extends, thus permanently elongating the inelastic layer and producing a composite fabric with elastic properties. This lamination and stretching process is advantageous in that utilizing elastic in an unstretched condition is easier and less expensive than stretched elastic used in traditional processing operations. However, one problem which has existed with presently available xe2x80x9czero-strainxe2x80x9d stretchable laminates Is surface abrasion. The mechanical stretching either fractures or disrupts the fibers within the substantially inelastic component of the xe2x80x9czero-strainxe2x80x9d laminate, and as a result, the fibers detach and are susceptible to linting and pilling. In addition, such fracturing or detachment causes a noticeable loss in fabric strength.
There have been attempts to address the aforementioned problems of fiber tie down and fabric abrasion resistance. For example, attempts have been made to make the nonwoven fabric component of the composite with high elongation properties. Conventional polypropylene, which has been widely used in producing nonwoven fabrics, provides adequate fuzz and abrasion resistance properties in the unstretched condition, but the elongation properties are unacceptable and therefore the fibers and/or fabrics fracture. Nonwoven webs formed from linear low density polyethylene (LLDPE) have been shown to have high elongation properties and also to possess excellent hand, softness and drape properties, as recognized for example in Fowells U.S. Pat. No. 4,644,045. However, such fabrics have not found wide commercial acceptance, since they fail to provide acceptable abrasion resistance. The bonding of LLDPE filaments into a spunbonded web with acceptable abrasion resistance has proven to be very difficult, since acceptable fiber tie down is observed at a temperature just below the point that the filaments begin to melt and stick to the calender. Because of this very narrow bonding window and the resulting abrasion resistance and fuzz properties, spunbonded LLDPE nonwovens have not found wide commercial acceptance for the aforementioned applications.
The present invention overcomes these disadvantages and limitations and provides a composite fine denier nonwoven fabric with a superior combination of extensibility, tensile properties and abrasion resistance. The composite nonwoven fabric of the present invention is comprised of at least two layers, the first layer containing multipolymer fibers with a plurality of bonds bonding the fibers together to form a coherent extensible nonwoven web. This coherent extensible nonwoven web has a Taber surface abrasion value (rubber wheel) of greater than 10 cycles and an elongation at peak load in at least one of the machine direction or the cross-machine direction of at least 70%. A second extensible layer is laminated to this coherent extensible nonwoven web.
The term xe2x80x9cfibersxe2x80x9d as used herein is intended to include both discrete length xe2x80x9cstaplexe2x80x9d fibers and continuous filaments. According to one embodiment of the present invention, the coherent extensible nonwoven web is a thermally bonded spunbond nonwoven web of randomly arranged substantially continuous filaments consisting of multiple polymers. According to another embodiment of the invention, the coherent extensible nonwoven web is a thermally bonded carded web of staple fibers. The coherent extensible nonwoven web may contain, in addition to the multipolymer fibers, additional fibrous components, such as meltblown microfibers. In accordance with the invention, the composite nonwoven fabric may include an optional third component laminated to the opposite side of the second extensible layer, which may, for example, be a film, another nonwoven web, or a composite fabric.
The second extensible layer to which the multipolymer fiber web is laminated can take various forms. For example, it may comprise a continuous or perforated polymer film, a film or web of an elastic polymer, another spunbonded nonwoven web, an extensible scrim or net, an array of extensible or elastic strands, or a web of meltblown microfibers. Where an elastic web or film is used, the composite can be stretch activated by elongation, which causes permanent elongation and stretching of the coherent extensible web of multipolymer fibers, and the resulting composite fabric exhibits elastic properties. Where an extensible nonelastic film layer is used, such as polyolefin film for example, the composite can be stretch activated by elongation to at least 20% of its original unstretched length, producing a composite having excellent softness and drape.